1. Field of the Invention
The present invention relates to a radio communication system, a radio communication method, and a base station, which include a serving cell transmitting an absolute grant and a relative grant to a radio terminal, and a non-serving cell transmitting the relative grant to the radio terminal without transmitting the absolute grant.
2. Description of the Related Art
Heretofore, a radio communication system including a base station and a radio network controller has been known. In the radio communication system, the base station has a single or multiple cells, and a radio communication is performed between each of the cells and a plurality of radio terminals. The radio network controller controls a plurality of base stations, and assigns radio resources to the plurality of radio terminals. Note that such a technique (hereinafter referred to as first technique) is sometimes referred to as R99 (Release 99) or the like.
For the purpose of improving the throughput and shortening the delay time, and the like, there has recently been proposed a technique in which a base station assigns the radio resources to uplink user data transmitted from each of the radio terminals to the base station (network side). Note that such a technique (hereinafter referred to as a second technique) is sometimes referred to as the high speed uplink packet access (HSUPA), the enhanced uplink (EUL) or the like.
Each of the cells functions as a serving cell or as a non-serving cell. A transport block size (TBS) is determined based on the transmission rate (for example, a scheduling grant (SG)) of the uplink user data, and is controlled by transmission rate control data transmitted from the serving cell and the non-serving cell. The transmission rate control data includes an absolute grant (AG) for controlling an absolute value of the transmission rate, and a relative grant (RG) for controlling a relative value of the transmission rate (for example, see 3GPP TS25.321 Ver. 7.5.0).
Here, the uplink user data is transmitted to the base station from the radio terminals via an enhanced dedicated physical data channel (E-DPDCH). The absolute grant (AG) is transmitted from the radio base station to the radio terminals via an E-DCH absolute grant channel (E-AGCH). The relative grant (RG) is transmitted from the radio base station to the radio terminals via an E-DCH relative grant channel (E-RGCH).
The serving cell transmits the absolute grant (AG) and the relative grant is (RG) to the radio terminals. Meanwhile, the non-serving cell transmits, to the radio terminals, only the relative grant (RG) without transmitting the absolute grant (AG).